My DIY 48V 16Ah battery cuts out at 47 Volts

[batteryGOLD]

As the title says, I built a battery pack 13s5p using LG MH1 cells salvaged from scooter batteries. I tested each cell on a Opus battery charger (on the 1A discharge setting) and they were all showing around the 3200mAh they are rated at, so it should be a 48V 16Ah battery. I built it to run a smaller bike with a 500watt geared front hub for a friend to ride and it worked well, although we never pushed it to its limit. I recently swapped my 1500w rear hub to a full suspension bike where there is no room to mount the big 52v20Ah battery I was using before, so I decided to give this battery a try.

What I am finding though is that I am getting far less range than with my bigger battery, like less than half the range, when this battery has 3/4 the Wh. (1040wh with the 52V triangle battery vs 768 Wh with this battery). The controller starts cutting out when the battery is still showing a resting voltage of 47v, according to this chart I found there should still be some capacity left.

Sir, I see you have at least two problems with your 13S battery

problem#1 --> S elements debalance
max is 4,20V (top cut point) & min is 3,93V (this element will make bms cut soon than others) --> soo it seems at this point U already lost about 25-30% capacity, so your estimated available capacity is about 16Ah x 0,7 equals 11,2Ah available.

problem #2 --> maybe reused cells with higher internal resistance mixed inside pack, you could have a week element anywhere from 13S elements. tha weakest link..(maybe #5S element or other or multiple elements affected, wish U luck to find iT)
the battery minimum voltage cut point should be 2,7V x 13 equals 35V , but your system cuts at 47V.. soo thats a huge difference
estimate capacity available at your battery calculate 47V/13S equals 3,62V (this means a 45% SOC state of charge ), soo thats 45% of battery unused , doin math 16Ah x 0,55 equals around 8,8Ah available, U could classify your 13S battery as a 9Ah battery grade B--- (I dont know letter grade scale, sorry..)

PS: problem#2 is dominant , so from 11,2Ah (problem #1) ,U only get ~8,8Ah
tha best ideia is simple, just build a new pack with new cells.. just sayin.. Do you want to have a low capacity battery and a risk of overheat or other risks?

"real good joke" consulting service TM,
have a nice day!

 

[spaceship]

Quick update, used a balance charger to bring cell group 5 up to 4.2v. I disconnected the bms wiring harness used some breadboard jumper wires pushed in to the bms wiring harness to charge the group through the bms wires.

I let it rest overnight and measured the group at 4.191v while the rest of the groups are sitting at either 4.22v or 4.23v. When I plug in the leads to the balancing bms board it gets warm to the touch, (not hot). I assume this is the passive balancing action, using the resistors to drain down the cells that are a few mV more until they match?

Im going to let it sit until the bms board is not passively balancing anymore (if its not warm to touch) then I'll measure again. If everything looks good I'll reassemble the case and run the battery through a few cycles, then Ill open it and check the balancing again.

Thanks!